170 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
Grind Size Optimisation for Carbon Capture
Optimisation of the grind size for carbon capture is a com-
plex balance between the carbonation kinetics on the one
hand and milling requirements on the other hand. In this
context, milling requirements incorporates both the equip-
ment requirements (e.g., equipment size, steel and concrete
used in construction) and the emissions from the actual
process (e.g., ore competency, hardness and abrasiveness).
This leads to a complex interplay between these various fac-
tors similar to those that determine the optimum grind size
for mineral recovery (e.g., liberation size weighed up against
recovery, Treatment Charges/Refining Charges (TC/RC)
and mill Capex/OPEX).
Testing is required to determine the carbonation degree
and kinetics. To the author’s knowledge currently there is
no standardised way to carry out this test, but it should
take a similar form to a grind size—recovery test, e.g., mill
feedstock to different sizes and determine the variables of
interest under standardised test conditions. Using the best-
fit exponential relationships for data published by Summers
et al. (2005) as a ‘pessimistic’ scenario, Gerdemann et al.
(2007) as an ‘intermediate’ scenario and data by Garcia et al.
(2010) as an ‘optimistic’ scenario, grind size optimisations
were carried out for the 100 t/h circuit described in this
paper. As implied in the first paragraph, this optimisation
trades off construction CO2 emissions based on bulk mate-
rials use, the effective carbon sequestration capacity of
olivine as a function of grind size and the variable CO2
emissions from the mining, milling and disposal of olivine.
Figure 6 shows the theoretical carbon capture capacity of
olivine as a function of grind size for these scenarios, and
Table 5 summarises the peak capture capacity as well as the
optimum grind size. Whilst there are differences between
the scenarios, they all point to an optimum grind size in
the 2–5 µm P80 range with peak sequestration capacities
of 0.45–0.53 t CO2/t olivine. The scenarios were qualified
depending on the grind size dependence of the carbonation
reaction (i.e., ‘pessimistic’ meaning the finest required grain
size for meaningful carbonation to occur). Therefore, the
grind size for the more optimistic scenarios is coarser. The
peak sequestration capacity is a function of the maximum
achievable CO2 sequestration capacity so this is less related
how the scenarios were qualified.
It is very important to bear in mind that this carbon
balance does not account for the energy consumption asso-
ciated with maintaining the high pressure and temperature
conditions required for the sequestration capacity. Rather,
it is intended to give an indication of the CO2 ‘budget’ for
the carbonation reaction.
0
0.1
0.2
0.3
0.4
0.5
0.6
1 10 100 1000
P
80
(μm)
Summers et al., 2005 (Pessimistic) Gerdemann et al., 2007 (Intermediate)
Garcia et al., 2010 (Optimistic)
Figure 6. Estimated net carbon sequestration capacity as a function of P80 for three scenarios
Carbon
capture
capacity
(t
CO/t
2
ore)
Grind Size Optimisation for Carbon Capture
Optimisation of the grind size for carbon capture is a com-
plex balance between the carbonation kinetics on the one
hand and milling requirements on the other hand. In this
context, milling requirements incorporates both the equip-
ment requirements (e.g., equipment size, steel and concrete
used in construction) and the emissions from the actual
process (e.g., ore competency, hardness and abrasiveness).
This leads to a complex interplay between these various fac-
tors similar to those that determine the optimum grind size
for mineral recovery (e.g., liberation size weighed up against
recovery, Treatment Charges/Refining Charges (TC/RC)
and mill Capex/OPEX).
Testing is required to determine the carbonation degree
and kinetics. To the author’s knowledge currently there is
no standardised way to carry out this test, but it should
take a similar form to a grind size—recovery test, e.g., mill
feedstock to different sizes and determine the variables of
interest under standardised test conditions. Using the best-
fit exponential relationships for data published by Summers
et al. (2005) as a ‘pessimistic’ scenario, Gerdemann et al.
(2007) as an ‘intermediate’ scenario and data by Garcia et al.
(2010) as an ‘optimistic’ scenario, grind size optimisations
were carried out for the 100 t/h circuit described in this
paper. As implied in the first paragraph, this optimisation
trades off construction CO2 emissions based on bulk mate-
rials use, the effective carbon sequestration capacity of
olivine as a function of grind size and the variable CO2
emissions from the mining, milling and disposal of olivine.
Figure 6 shows the theoretical carbon capture capacity of
olivine as a function of grind size for these scenarios, and
Table 5 summarises the peak capture capacity as well as the
optimum grind size. Whilst there are differences between
the scenarios, they all point to an optimum grind size in
the 2–5 µm P80 range with peak sequestration capacities
of 0.45–0.53 t CO2/t olivine. The scenarios were qualified
depending on the grind size dependence of the carbonation
reaction (i.e., ‘pessimistic’ meaning the finest required grain
size for meaningful carbonation to occur). Therefore, the
grind size for the more optimistic scenarios is coarser. The
peak sequestration capacity is a function of the maximum
achievable CO2 sequestration capacity so this is less related
how the scenarios were qualified.
It is very important to bear in mind that this carbon
balance does not account for the energy consumption asso-
ciated with maintaining the high pressure and temperature
conditions required for the sequestration capacity. Rather,
it is intended to give an indication of the CO2 ‘budget’ for
the carbonation reaction.
0
0.1
0.2
0.3
0.4
0.5
0.6
1 10 100 1000
P
80
(μm)
Summers et al., 2005 (Pessimistic) Gerdemann et al., 2007 (Intermediate)
Garcia et al., 2010 (Optimistic)
Figure 6. Estimated net carbon sequestration capacity as a function of P80 for three scenarios
Carbon
capture
capacity
(t
CO/t
2
ore)